The present invention is generally in the field of measurement techniques, and relates to a method and system for model-based analysis of measured data. The invention is particularly useful for metrology systems for interpreting scatterometry measurements in patterned structures, such as semiconductor wafers.
Advanced processes and integration schemes (such as those utilizing multi-patterning and FinFET technologies) require precise detection and control of intricate profile parameters on a complex structures such as the sidewall angle, spacer widths, spacer pull-down, epitaxial proximity, footing/undercut, overfill/underfill parameters, etc. Scatterometry is known as the primary non-destructive method to address such detailed requirements for in-line profile metrology. Optical Critical Dimension (also termed “optical CD” or “OCD”) measurement techniques (known also as Scatterometry) are known as efficient techniques for measuring parameters of patterned (periodic) structures. Measurement of these parameters provides a viable metrology solution for process control in high volume manufacturing of semiconductor devices.
Scatterometry is a model-based technique for optical critical dimension measurements (also termed “optical CD” or “OCD”) in patterned structures enabling real-time monitoring of a patterning process. OCD measurements are usually performed using a fitting procedure. According to this procedure, theoretical model describing a structure under measurements is used to generate theoretical data or reference data, and the latter is iteratively compared to measured data, while varying the model parameters until the “best fit” is found. The parameters of the “best fit” model are considered as corresponding to the measured parameters. Measured data (typically optical data) can be analyzed to derive information regarding the geometrical parameters of patterns including thicknesses, critical dimension (CD), line spacing, line width, wall depth, wall profile, etc., as well as optical constants of materials included in a sample being measured.
Various model-based techniques have been developed for interpretation of the measured data. Such techniques are described for example in the following patent publications US2013124141, US2013282343, US2014195194, US2014142869, all assigned to the assignee of the present application.